In order to maintain a superconductive cable or the like in an ultra-low temperature state, there has been known a technique for supplying ultra-low temperature liquid such as liquid nitrogen to a vacuum insulated tube in which the superconductive cable or the like is housed. A liquid supply (circulation) system for ultra-low temperature liquid constantly supplies the ultra-low temperature liquid into the vacuum insulated tube in order to maintain the superconductive cable in a superconductive state in an apparatus to be cooled, in which the superconductive cable is provided in the vacuum insulated tube.
The ultra-low temperature liquid circulation system has been often used assuming that only liquid is circulated. As a pump mechanism in that case, representatively, a centrifugal pump has been often used. However, as a use, it is also conceivable to transfer ultra-low temperature slurry liquid including solid particles of metal powder, stone, ceramic, and the like. An ultra-low temperature liquid circulation system adapted to the ultra-low temperature slurry liquid is demanded.
Since the centrifugal pump has a relatively low discharge pressure, it is difficult to supply high-concentration slurry. Since rotating components such as an impeller has large relative speed to slurry, the rotating components have large fictional forces and are easily worn. The rotating components bite solid particles in gaps of rotating sections to be easily locked. As a pump configuration that can realize a higher discharge pressure than the centrifugal pump, there is known a bellows pump for ultra-low temperature including a bellows member made of metal (PTL 1). However, when a liquid feed target is liquid including slurry, it is likely that the slurry hits the bellows made of metal to damage the bellows and is bitten in a bellows portion to damage a metal material.
As a liquid supply system that uses transfer liquid including a depositing material such as slurry, there is known a liquid supply system including a bellows made of resin (PTL 2). However, in the case of a pump made of resin, flexibility is poor and a stroke amount cannot be secured compared with a metal material. Therefore, it is hard to obtain pump performance necessary for supplying liquid at a large flow rate. The pump made of resin is more likely to be buckled compared with the metal material.
As measures against the slurry, there has been known a method of coating a liquid contact part of a liquid supply system with elastomer having elasticity such as rubber. Since a shock of the slurry such as solid particles is reduced by the coating having elasticity, abrasion resistance is shown against the slurry near the room temperature. However, under an ultra-low temperature environment equal to or lower than a glass transition point, since the rubber changes to a glass state and loses elasticity, the rubber does not have abrasion resistance to low-temperature slurry.